Conventional bicycle drive trains utilize a chain drive composed of a chain and sprockets to transfer motion from the pedals to the rear wheel of the bicycle. The disadvantages associated with chain drives are the exposure of the lubricated parts to contamination, causing excessive wear to interfacing parts and causing poor function, to complete failure, of operation. To prevent this requires frequent cleaning.
Another disadvantage is the exposure of the meshing point of the chain and sprocket, leaving it open to debris to be caught between the chain and sprocket rendering the system inoperable. The position of the rear derailleur makes it susceptible to strikes from obstacles occurred on roads or off-road trails. The chain can be thrown from the sprocket during operation on harsh road or trail conditions, again rendering it inoperable. The large front sprockets, in conjunction with the position and movement of the rear derailleur, spreads out the space required for such systems. This makes them cumbersome to enclose in order to shield from contamination. In prior art there are several shaft drives which have been proposed and are considered.
Drive shaft systems as described in U.S. Pat. Nos. 5,622,081, 5,342,075, and 5,228,354 require that pedaling stops in order to shift to a different gear ratio. In '081 and '354, the system is disengaged with the use of a clutching mechanism that disengages a pinion gear from a face gear. In '081, '354, and U.S. Pat. No. 3,863,503 there are two separate gear shift controls, one for the front and one for the rear, that shift these mechanisms. Each of '081, '075, '354, '503, and U.S. Pat. No. 5,251,504 require a bracket type of connection from the drive shaft system to the bicycle's frame, requiring every frame design to consider this requirement. None of these prior art drive shaft systems consider frames designed for rear suspension and the requirements therein.
It would be advantageous for a drive shaft system to include the ability to shift while pedaling the bicycle. It would also be advantageous to attach a drive shaft system independent of the bicycle frame. It would be advantageous to simplify the gear shift controls.